Solar Panels on Pre-1920 Homes

What characterises a pre-1920 roof

Houses built before the First World War were roofed in natural slate or handmade clay, laid over sawn timber that was sized by rule of thumb rather than calculation. A century of repairs, extensions, re-covering and loft conversions sits on top of that. No two are the same, and very little about them is standard.

That is the honest starting point. A survey on a house of this age tells us more than on any other type of property, because almost nothing can be assumed from the outside.

Covering and structure

Natural slate is thin, brittle and holed rather than nibbed. It cannot be lifted and relieved the way an interlocking tile can, so hooks for slate work differently and the number of slates disturbed has to be kept to a minimum. Nail sickness is common on roofs of this age — the fixings corrode long before the slate itself fails — and a roof that is close to needing re-covering is better re-covered first, with the array going on afterwards.

Handmade clay peg and plain tiles are similarly fragile and considerably more fiddly than modern interlocking tile.

Underneath, rafter centres wander. Spacings of anything from 300mm to well over 500mm turn up on the same slope, sometimes because of an old repair, sometimes because that is simply how it was cut. Sections can be light by modern standards, and we regularly find timbers weakened by past notching for services, historic water ingress or beetle. Rail-based mounting handles irregular centres, but only once the centres have actually been measured.

Electrical implications

The array is the easy half. On a house of this age the consumer unit is frequently the constraint — an older board with no spare ways, no RCD protection, or a rewireable fuse carrier that is not a sensible thing to connect a generation circuit to. Main earthing and bonding often predate current requirements, particularly where a supply has been altered piecemeal.

None of that is unusual and none of it is a reason not to proceed. It does need pricing honestly at survey rather than appearing as a variation on install day. Main fuse rating also matters, especially if a battery and an EV charger are planned alongside.

Design, layout and mounting

Chimney stacks, valleys, dormers and parapets carve these roofs into small usable rectangles. A design that ignores them looks wrong and shades itself. We set panels back from verges and ridges, work around stacks rather than under them, and accept a smaller array where the alternative is an ugly one.

In-roof mounting is worth considering here. It sits the panels flush with the slate line, which is often what makes an array acceptable on a prominent elevation, and it suits a roof being re-covered anyway. All-black panels with black frames read far better against slate than silver framing.

Access and limitations

Terraced frontages, narrow side alleys, on-street parking and high ridges all make scaffolding more involved and more expensive than on a modern estate house. Where access needs a pavement licence from the highway authority, that takes lead time.

The limitations are real. Some pre-1920 roofs are not worth loading until they are re-covered. Some frontages should not carry panels at all. Where that is the case, a rear slope, an outbuilding or a garden array is usually the better conversation.